Supreme Court Chief Justice John G. Roberts Jr. certainly sounded authoritative when he made a striking, though unflattering, declaration about Massachusetts as the high court heard arguments over the Voting Rights Act of 1965, which is designed to assure equal access across races to polling booths.

“Do you know which state has the worst ratio of white voter turnout to African-American voter turnout?” Roberts asked Donald Verrilli Jr., solicitor general for the Department of Justice, during Wednesday’s arguments.

“Massachusetts,” Roberts responded, adding that even Mississippi has a narrower gap.

Roberts later asked if Verrilli knew which state has the greatest disparity in registration. Again, Roberts said it was Massachusetts.

The problem is, Roberts is woefully wrong on those points, according to Massachusetts Secretary of State William F. Galvin, who on Thursday branded Roberts’s assertion a slur and made a declaration of his own. “I’m calling him out,” Galvin said.

Galvin was not alone in his view. Academics and Massachusetts politicians said that Roberts appeared to be misguided. A Supreme Court spokeswoman declined to offer supporting evidence of Roberts’s view, referring a reporter to the court transcript.

On Thursday,
Galvin tried to set the record straight. “We have one of the highest voter registrations in the country,” he said, “so this whole effort to make a cheap-shot point at Massachusetts is deceptive.”

Shelby County, Ala., is challenging a provision of the Voting Rights Act that requires nine states, mostly in the South, to seek permission from federal officials before changing voting procedures. Those states argue that the restrictions are unfair, and Roberts seemed to agree, appearing to use Massachusetts as an example of states that have been exempt from certain provisions of the act, yet less successful in providing ballot access.

“In the state of Massachusetts, we’ve seen a great increase in voter participation in communities of color, particularly among African-Americans, Latinos, and Asians,” said Boston city councilor Tito Jackson, who served as political director for Governor Deval Patrick’s most recent campaign.

In the November 2012 election, there was little difference in voter turnout in Boston neighborhoods with high concentrations of white or black voters. In Charlestown, where 80 percent of residents are white, 68 percent of voters cast ballots in November. In Roxbury, the traditional heart of Boston’s African-American community, about 64 percent of voters came out to the polls.

Galvin and political scientists speculated that Roberts drew his conclusions using US Census Bureau data known as “The Current Population Survey,” which collects information on voting and registration every other year. Political scientists say this is one of the few national databases, if not the only one, providing state-by-state voting information.

But a review of those census data appears to contradict Roberts, showing such states as Washington, Arizona, and Minnesota with similar if not bigger gaps between black and white voters.

“The concept of black communities in Massachusetts not voting is an old slur, and it’s not true,” Galvin said. “I guess the point [Roberts] is trying to make is Mississippi is doing so much better they don’t need the Voting Rights Act. He can still relay that conclusion, but he shouldn’t be using phony statistics. It’s deceptive, and it’s truly disturbing.”

According to the census figures, a larger percentage of blacks voted in Mississippi than whites, one percentage point more.

But political scientists caution against drawing sweeping conclusions from the census survey or using it to compare states. The black population in nearly one-fourth of states surveyed in 2010 was so small that it was not possible to make statistically reliable comparisons. And the margin of error for nearly another quarter of the states, including Massachusetts, was in the double digits.

“The margin of error is huge,” said Michael P. McDonald, a professor of government and politics at George Mason University who specializes in American elections. “They’re not reliable numbers.”

That’s not to say Massachusetts or states and municipalities north of the Mason-Dixon Line are bastions of voting equality that do not need the scrutiny that comes with the Voting Rights Act.

Brooklyn, Manhattan, and the Bronx are subject to Section 5 of the law, which requires US oversight.

When scrutinizing voter turnout numbers, political scientists said it is imperative to look at those figures in the context of the election being held. Was it a national, state, or local election? Was it a midterm election? Did the candidates heavily court voters within communities of color? And what is the make-up of the black community, citizens registered to vote or immigrants who have not become citizens? Otherwise, the numbers exist in isolation, analysts said.

It would be disingenuous to compare elections in Massachusetts and Mississippi, said James Jennings of Tufts, because they take place in different contexts. The two states have a different set of challenges based on region, history, and populations.

He cited the election of Elizabeth Warren to the US Senate. Warren courted voters of color, unlike the 2010 special election to fill the seat of the late Edward M. Kennedy, a race that pitted Republican Scott Brown against Democrat Martha Coakley.

“They both ignored black and Latino voters,” Jennings said.

So, he said, the gap between voters of color and white voters was probably bigger.